Preheat oven to 325 degrees F. Grease a glass pie dish (9.5 inches, 24cm) with butter.
Place all the ingredients in the food processor. Process until combined.
Transfer the thick batter to the prepared baking dish. Smooth the top with a spatula, or with your hands. Bake 40 minutes, then carefully shield the edges with foil strips and continue baking 10 more minutes, or until browned and fragrant and a toothpick inserted in the center comes out clean.
Cool in pan on a cooling rack 10 minutes, then invert onto a cutting board and back onto the cooling rack. Let cool 20 more minutes before slicing and serving. Leftovers keep several days in the fridge. Remove from fridge 30 minutes before serving.